Breaking in our new test system is a wide variety of both AMD and Nvidia graphics cards from the past few years, ranging from entry level passively cooled cards to high performance models with large, non-reference coolers.

TEST RESULTS

Power Consumption

The power consumption of an add-on video card can be estimated by comparing the total system power draw with and without the card installed. Our results were derived thus:

1. Power consumption of the graphics card at idle  when Prime95 is run on a system, the video card is not stressed at all and stays idle. This is true whether the video card is integrated or an add-on PCIe 16X device. Hence, when the power consumption of the base system under Prime95 is subtracted from the power consumption of the same test with the graphics card installed, we obtain the increase in idle power of the add-on card over the integrated graphics chip.

2. Power consumption of the graphics card under load  the power draw of the system is measured with the add-on video card, with Prime95 and FurMark running simultaneously. Then the power of the baseline system (with integrated graphics) running just Prime95 is subtracted. The difference is the load power of the add-on card. Any load on the CPU from FurMark should not skew the results, since the CPU was running at full load in both systems.

Both results are scaled by the efficiency of the power supply (tested here) to obtain a final estimate of the DC power consumption.

Note: the actual power of the add-on card cannot be derived using this method because the integrated graphics may draw some power even when not in use. However, the relative difference between the cards should be accurate.

The energy efficiency of modern day graphics cards is quite good. With the exception of the few high performance models in our roundup, most of the cards idle using less than 15W. On load, the HIS HD 5870 had the highest draw of 236W, one of the reasons its our reference card for GPU heatsink testing. Also note that both the HD 6870 and HD 5870 were tested using the GELID Icy Vision, an excellent third party cooler with its fans running at 5V (~1260 RPM), possibly skewing their results slightly as better cooling increases overall energy efficiency.

The cards tested had very similar CPU usage during video playback, 1~2% for our 1080p H.264/MKV test clip, and 8~9% for our YouTube HD sample. Power consumption however varied greatly, dependent mostly on the core/memory clocks used by the cards' respective video decoder chips. The higher-end HD 5000/6000 series cards are particularly prone to this issue, being substantially more power hungry than their low-end counterparts and competitors on the Nvidia side.

The GTX 680 is especially impressive in this regard, consuming only 6~8W more than its idle usage while the HD 5870 and HD 6870 produced an increase four to five times higher.